Method and apparatus for determining handover of user equipments attached to mobile relay nodes in wireless communication system

ABSTRACT

A method and apparatus for determining handover of user equipments (UEs) attached to a mobile relay node (RN), which is moving from a source DeNB to the target DeNB, in a wireless communication system is provided. A target donor eNodeB (DeNB) receives a handover request message, and receives an indication including UE context of the UEs attach to the mobile relay node. The target DeNB determines whether to accept or reject the handover of each UE.

TECHNICAL FIELD

The present invention relates to wireless communication, and moreparticularly, to a method and apparatus for determining handover of userequipments access to mobile relay nodes in wireless communicationsystem.

BACKGROUND ART

Universal mobile telecommunications system (UMTS) is a 3rd generation(3G) asynchronous mobile communication system operating in wideband codedivision multiple access (WCDMA) based on European systems, globalsystem for mobile communications (GSM) and general packet radio services(GPRS). The long-term evolution (LTE) of UMTS is under discussion by the3rd generation partnership project (3GPP) that standardized UMTS.

The 3GPP LTE is a technology for enabling high-speed packetcommunications. Many schemes have been proposed for the LTE objectiveincluding those that aim to reduce user and provider costs, improveservice quality, and expand and improve coverage and system capacity.The 3GPP LTE requires reduced cost per bit, increased serviceavailability, flexible use of a frequency band, a simple structure, anopen interface, and adequate power consumption of a terminal as anupper-level requirement.

FIG. 1 shows network structure of an evolved universal mobiletelecommunication system (E-UMTS). The E-UMTS may be also referred to asan LTE system. The communication network is widely deployed to provide avariety of communication services such as voice over internet protocol(VoIP) through IMS and packet data.

As illustrated in FIG. 1, the E-UMTS network includes an evolved UMTSterrestrial radio access network (E-UTRAN), an evolved packet core (EPC)and one or more user equipment. The E-UTRAN may include one or moreevolved NodeB (eNB) 20, and a plurality of user equipment (UE) 10. Oneor more E-UTRAN mobility management entity (MME)/system architectureevolution (SAE) gateways (S-GW) 30 may be positioned at the end of thenetwork and connected to an external network.

As used herein, “downlink” refers to communication from eNB 20 to UE 10,and “uplink” refers to communication from the UE to an eNB. UE 10 refersto communication equipment carried by a user and may be also referred toas a mobile station (MS), a user terminal (UT), a subscriber station(SS) or a wireless device.

An eNB 20 provides end points of a user plane and a control plane to theUE 10. MME/S-GW 30 provides an end point of a session and mobilitymanagement function for UE 10. The eNB and MME/S-GW may be connected viaan S1 interface.

The eNB 20 is generally a fixed station that communicates with a UE 10,and may also be referred to as a base station (BS) or an access point.One eNB 20 may be deployed per cell. An interface for transmitting usertraffic or control traffic may be used between eNBs 20.

The MME provides various functions including non-access stratum (NAS)signaling to eNBs 20, NAS signaling security, access stratum (AS)security control, Inter core network (CN) node signaling for mobilitybetween 3GPP access networks, Idle mode UE reachability (includingcontrol and execution of paging retransmission), tracking area listmanagement (for UE in idle and active mode), packet data network (PDN)GW and serving GW selection, MME selection for handovers with MMEchange, serving GPRS support node (SGSN) selection for handovers to 2Gor 3G 3GPP access networks, roaming, authentication, bearer managementfunctions including dedicated bearer establishment, support for publicwarning system (PWS) (which includes earthquake and tsunami warningsystem (ETWS) and commercial mobile alert system (CMAS)) messagetransmission. The S-GW host provides assorted functions includingper-user based packet filtering (by e.g. deep packet inspection), lawfulinterception, UE internet protocol (IP) address allocation, transportlevel packet marking in the downlink, UL and DL service level charging,gating and rate enforcement, DL rate enforcement based on APN-AMBR. Forclarity MME/S-GW 30 will be referred to herein simply as a “gateway,”but it is understood that this entity includes both an MME and an SAEgateway.

A plurality of nodes may be connected between eNB 20 and gateway 30 viathe S1 interface. The eNBs 20 may be connected to each other via an X2interface and neighboring eNBs may have a meshed network structure thathas the X2 interface.

FIG. 2 shows architecture of a typical E-UTRAN and a typical EPC.

As illustrated, eNB 20 may perform functions of selection for gateway30, routing toward the gateway during a radio resource control (RRC)activation, scheduling and transmitting of paging messages, schedulingand transmitting of broadcast channel (BCH) information, dynamicallocation of resources to UEs 10 in both uplink and downlink,configuration and provisioning of eNB measurements, radio bearercontrol, radio admission control (RAC), and connection mobility controlin LTE_ACTIVE state. In the EPC, and as noted above, gateway 30 mayperform functions of paging origination, LTE_IDLE state management,ciphering of the user plane, SAE bearer control, and ciphering andintegrity protection of NAS signaling.

FIG. 3 shows a user-plane protocol and a control-plane protocol stackfor the E-UMTS.

FIG. 3( a) is block diagram depicting the user-plane protocol, and FIG.3( b) is block diagram depicting the control-plane protocol. Asillustrated, the protocol layers may be divided into a first layer (L1),a second layer (L2) and a third layer (L3) based upon the three lowerlayers of an open system interconnection (OSI) standard model that iswell known in the art of communication systems.

The physical layer, the L1, provides an information transmission serviceto an upper layer by using a physical channel. The physical layer isconnected with a medium access control (MAC) layer located at a higherlevel through a transport channel, and data between the MAC layer andthe physical layer is transferred via the transport channel. Betweendifferent physical layers, namely, between physical layers of atransmission side and a reception side, data is transferred via thephysical channel.

The MAC layer of the L2 provides services to a radio link control (RLC)layer (which is a higher layer) via a logical channel. The RLC layer ofthe L2 supports the transmission of data with reliability. It should benoted that the RLC layer illustrated in FIGS. 3( a) and 3(b) is depictedbecause if the RLC functions are implemented in and performed by the MAClayer, the RLC layer itself is not required. A packet data convergenceprotocol (PDCP) layer of the L2 performs a header compression functionthat reduces unnecessary control information such that data beingtransmitted by employing IP packets, such as IPv4 or IPv6, can beefficiently sent over a radio (wireless) interface that has a relativelysmall bandwidth.

A radio resource control (RRC) layer located at the lowest portion ofthe L3 is only defined in the control plane and controls logicalchannels, transport channels and the physical channels in relation tothe configuration, reconfiguration, and release of the radio bearers(RBs). Here, the RB signifies a service provided by the L2 for datatransmission between the terminal and the UTRAN.

As illustrated in FIG. 3( a), the RLC and MAC layers (terminated in aneNB 20 on the network side) may perform functions such as scheduling,automatic repeat request (ARQ), and hybrid automatic repeat request(HARQ). The PDCP layer (terminated in eNB 20 on the network side) mayperform the user plane functions such as header compression, integrityprotection, and ciphering.

As illustrated in FIG. 3( b), the RLC and MAC layers (terminated in aneNodeB 20 on the network side) perform the same functions for thecontrol plane. As illustrated, the RRC layer (terminated in an eNB 20 onthe network side) may perform functions such as broadcasting, paging,RRC connection management, RB control, mobility functions, and UEmeasurement reporting and controlling. The NAS control protocol(terminated in the MME of gateway 30 on the network side) may performfunctions such as a SAE bearer management, authentication, LTE_IDLEmobility handling, paging origination in LTE_IDLE, and security controlfor the signaling between the gateway and UE 10.

The RRC state may be divided into two different states such as aRRC_IDLE and a RRC_CONNECTED. In RRC_IDLE state, the UE 10 may receivebroadcasts of system information and paging information while the UEspecifies a discontinuous reception (DRX) configured by NAS, and the UEhas been allocated an identification (ID) which uniquely identifies theUE in a tracking area and may perform PLMN selection and cellre-selection. Also, in RRC_IDLE state, no RRC context is stored in theeNB.

In RRC_CONNECTED state, the UE 10 has an E-UTRAN RRC connection and acontext in the E-UTRAN, such that transmitting and/or receiving datato/from the network (eNB) becomes possible. Also, the UE 10 can reportchannel quality information and feedback information to the eNB.

In RRC_CONNECTED state, the E-UTRAN knows the cell to which the UE 10belongs. Therefore, the network can transmit and/or receive data to/fromUE 10, the network can control mobility (handover and inter-radio accesstechnologies (RAT) cell change order to GSM EDGE radio access network(GERAN) with network assisted cell change (NACC)) of the UE, and thenetwork can perform cell measurements for a neighboring cell.

In RRC_IDLE state, the UE 10 specifies the paging DRX cycle.Specifically, the UE 10 monitors a paging signal at a specific pagingoccasion of every UE specific paging DRX cycle.

The paging occasion is a time interval during which a paging signal istransmitted. The UE 10 has its own paging occasion.

A paging message is transmitted over all cells belonging to the sametracking area. If the UE 10 moves from one tracking area to anothertracking area, the UE will send a tracking area update message to thenetwork to update its location.

FIG. 4 shows an example of structure of a physical channel.

The physical channel transfers signaling and data between layer L1 of aUE and eNB. As illustrated in FIG. 4, the physical channel transfers thesignaling and data with a radio resource, which consists of one or moresub-carriers in frequency and one more symbols in time.

One sub-frame, which is 1 ms in length, consists of several symbols. Theparticular symbol(s) of the sub-frame, such as the first symbol of thesub-frame, can be used for downlink control channel (PDCCH). PDCCHscarry dynamic allocated resources, such as PRBs and modulation andcoding scheme (MCS).

A transport channel transfers signaling and data between the L1 and MAClayers. A physical channel is mapped to a transport channel.

Downlink transport channel types include a broadcast channel (BCH), adownlink shared channel (DL-SCH), a paging channel (PCH) and a multicastchannel (MCH). The BCH is used for transmitting system information. TheDL-SCH supports HARQ, dynamic link adaptation by varying the modulation,coding and transmit power, and both dynamic and semi-static resourceallocation. The DL-SCH also may enable broadcast in the entire cell andthe use of beamforming. The PCH is used for paging a UE. The MCH is usedfor multicast or broadcast service transmission.

Uplink transport channel types include an uplink shared channel (UL-SCH)and random access channel(s) (RACH). The UL-SCH supports HARQ anddynamic link adaptation by varying the transmit power and potentiallymodulation and coding. The UL-SCH also may enable the use ofbeamforming. The RACH is normally used for initial access to a cell.

The MAC sublayer provides data transfer services on logical channels. Aset of logical channel types is defined for different data transferservices offered by MAC. Each logical channel type is defined accordingto the type of information transferred.

Logical channels are generally classified into two groups. The twogroups are control channels for the transfer of control planeinformation and traffic channels for the transfer of user planeinformation.

Control channels are used for transfer of control plane informationonly. The control channels provided by MAC include a broadcast controlchannel (BCCH), a paging control channel (PCCH), a common controlchannel (CCCH), a multicast control channel (MCCH) and a dedicatedcontrol channel (DCCH). The BCCH is a downlink channel for broadcastingsystem control information. The PCCH is a downlink channel thattransfers paging information and is used when the network does not knowthe location cell of a UE. The CCCH is used by UEs having no RRCconnection with the network. The MCCH is a point-to-multipoint downlinkchannel used for transmitting MBMS control information from the networkto a UE. The DCCH is a point-to-point bi-directional channel used by UEshaving an RRC connection that transmits dedicated control informationbetween a UE and the network.

Traffic channels are used for the transfer of user plane informationonly. The traffic channels provided by MAC include a dedicated trafficchannel (DTCH) and a multicast traffic channel (MTCH). The DTCH is apoint-to-point channel, dedicated to one UE for the transfer of userinformation and can exist in both uplink and downlink. The MTCH is apoint-to-multipoint downlink channel for transmitting traffic data fromthe network to the UE.

Uplink connections between logical channels and transport channelsinclude a DCCH that can be mapped to UL-SCH, a DTCH that can be mappedto UL-SCH and a CCCH that can be mapped to UL-SCH. Downlink connectionsbetween logical channels and transport channels include a BCCH that canbe mapped to BCH or DL-SCH, a PCCH that can be mapped to PCH, a DCCHthat can be mapped to DL-SCH, and a DTCH that can be mapped to DL-SCH, aMCCH that can be mapped to MCH, and a MTCH that can be mapped to MCH.

3GPP LTE-A may supports relaying by having a relay node (RN) wirelesslyconnect to an eNB serving the RN. It may be referred to paragraph 4.7 of3rd generation partnership project (3GPP) TS 36.300 V10.2.0 (2010-12).

FIG. 5 shows an objective of relay.

Referring to FIG. 5, a relay node (RN) wirelessly communicates with aneNB supporting relay, and thus can support capacity assistance of ashadow region or coverage extension through a service for UEs located ina cell boundary region and outside the boundary region. The eNB servingthe RN may be referred as a donor eNB (DeNB). The DeNB requires severaladditional functions for supporting relay. When there is an access ofthe relay node, the DeNB can perform a reconfiguration task to provideinformation required for relay and system information through dedicatedsignaling. The DeNB and the RN may be connected via a modified versionof the E-UTRA radio interface. The modified version may be referred as aUn interface.

The RN may support eNB functionality. It means that the RN terminatesthe radio protocols of the E-UTRA radio interface, and S1 and X2interfaces. In addition to the eNB functionality, the RN may alsosupport a subset of UE functionality, e.g., a physical layer, layer-2,RRC, and NAS functionality, in order to wirelessly connect to the DeNB.That is, the relay node can operate as a relay-type UE with respect tothe DeNB, and can operate as an eNB with respect to a served UE.

FIG. 6 shows an overall E-UTRAN architecture supporting relay nodes.

Referring to FIG. 6, the LTE-A network includes an E-UTRAN, an EPC andone or more user equipment (not described). The E-UTRAN may include oneor more relay node (RN) 50, one or more DeNB 60, one or more eNB 61 anda plurality of UE may be located in one cell. One or more E-UTRANMME/S-GW 70 may be positioned at the end of the network and connected toan external network.

As used herein, “downlink” refers to communication from the eNB 61 tothe UE, from the DeNB 60 to the UE or from the RN 50 to the UE, and“uplink” refers to communication from the UE to the eNB 61, from the UEto the DeNB 60 or from the UE to the RN 50. The UE refers tocommunication equipment carried by a user and may be also referred to asa mobile station (MS), a user terminal (UT), a subscriber station (SS)or a wireless device.

The eNB 61 and the DeNB 60 provide end points of a user plane and acontrol plane to the UE. The MME/S-GW 70 provides an end point of asession and mobility management function for UE. The eNB 61 and theMME/S-GW 70 may be connected via an S1 interface. The DeNB 60 andMME/SAE gateway 70 may be connected via an S1 interface. The eNBs 61 maybe connected to each other via an X2 interface and neighboring eNBs mayhave a meshed network structure that has the X2 interface. The eNB 61and the DeNB 60 may be connected to each other via an X2 interface.

The RN 50 may be wirelessly connected to the DeNB 60 via a modifiedversion of the E-UTRA radio interface being called the Un interface.That is, the RN 50 may be served by the DeNB 60. The RN 50 may supportthe eNB functionality which means that it terminates the S1 and X2interfaces. Functionality defined for the eNB 61 or the DeNB 60, e.g.radio network layer (RNL) and transport network layer (TNL), may alsoapply to RNs 50. In addition to the eNB functionality, the RN 50 mayalso support a subset of the UE functionality, e.g. physical layer,layer-2, RRC, and NAS functionality, in order to wirelessly connect tothe DeNB 60.

The RN 50 may terminate the S1, X2 and Un interfaces. The DeNB 60 mayprovide S1 and X2 proxy functionality between the RN 50 and othernetwork nodes (other eNBs, MMEs and S-GWs). The S1 and X2 proxyfunctionality may include passing UE-dedicated S1 and X2 signalingmessages as well as GTP data packets between the S1 and X2 interfacesassociated with the RN 50 and the S1 and X2 interfaces associated withother network nodes. Due to the proxy functionality, the DeNB 60 appearsas an MME (for S1) and an eNB (for X2) to the RN 50.

The DeNB 60 may also embed and provides the S-GW/P-GW-like functionsneeded for the RN operation. This includes creating a session for the RN50 and managing EPS bearers for the RN 50, as well as terminating theS11 interface towards the MME serving the RN 50.

The RN 50 and the DeNB 60 may also perform mapping of signaling and datapackets onto EPS bearers that are setup for the RN. The mapping may bebased on existing QoS mechanisms defined for the UE and the P-GW.

The relay node may be classified to a fixed relay node and a mobilerelay node. The mobile relay node may be applied to the 3GPP LTE rel-11.One of the possible deployment scenarios of mobile relay node is highspeed public transportation, e.g, a high speed railway. That is, themobile relay node may be put on the top of a high speed train. Hence, itis easily expected that the provision of various good quality servicestowards the users on a high speed public transportation will beimportant. Meanwhile, the service requirements offered by the fixedrelay node seem to be different from those offered by the mobile relaynode. So, there might be a few of considerations that should be resolvedin the mobile relay node. The solutions to resolve these considerationsfor mobile relay node may have impacts on a radio access network (RAN).

FIG. 7 shows an example of deployments scenario of mobile relay node ata high speed train.

Referring to FIG. 7, a mobile relay node is installed in a high speedtrain. A coverage of the mobile relay node may correspond to theentirety of the high speed train or each of cars constituting the highspeed train. The mobile relay node can communicate with UEs in the highspeed train through an access link. At present, the mobile relay node isin a coverage of an eNB1 supporting relay. The mobile relay node cancommunicate with the eNB1 through a backhaul link. When the high speedtrain moves, the mobile relay node may enter a coverage of an eNB2supporting relay. Accordingly, the mobile relay node can be handed overfrom the eNB1 to the eNB2.

Various mobile relay architectures for supporting the mobile relay nodemay be proposed. It is natural that all of mobile relay architecturesfocus on how to provide the RN handover. Nevertheless, it is importantto consider the handover for UEs connected to the mobile relay node,analyzing the proposed mobile relay architectures.

FIG. 8 shows an example of a mobile relay node architecture.

Referring to FIG. 8, a mobile relay node has both an eNB network elementand a UE network element. That is, the mobile relay node supports eNBfunctionalities and UE functionalities. Also, a SGW/PGW of the mobilerelay node is located at a core network, not in a DeNB supporting themobile relay node. In this case, the DeNB supporting the mobile relaynode cannot know the control signal and the data traffic related to theUEs connected to the mobile relay node. It is because that an S1interface and the signaling connections are spanning from the SGW/PGW ofthe mobile relay node to the mobile relay node through the DeNBtransparently and a packet destined to the UEs is encapsulated into thestream control transmission protocol/GPRS tunneling protocol (SCTP/GTP)spanned between SGW/PGW of the mobile relay node and the mobile relaynode.

FIG. 9 shows another example of a mobile relay node architecture.

Referring to FIG. 9, a mobile relay node has both an eNB network elementand a UE network element. That is, the mobile relay node supports eNBfunctionalities and UE functionalities. Also, a SGW/PGW of the mobilerelay node and an optional relay GW are located in a DeNB where themobile relay node attaches for normal operation to support the mobilerelay. In this case, the DeNB supporting the mobile relay node can knowthe control signal and the data traffic related to the UEs connected tothe mobile relay node. It is because that the DeNB is able to interpretthe control signal and the data traffic related to the UEs passingthrough the DeNB.

In LTE Rel-8 UE handover, a target eNB accepts or rejects a UE whichattempts a handover according to its current situation, e.g. amounts ofassignable resources, the channel environment for a Uu interface, etc,using a UE context. In the same manner, a target DeNB which support amobile relay node should use a RN context to decide an RN handover.Besides, the target DeNB should support a group mobility for UEsconnected to the mobile relay node. Accordingly, the RN handover from asource DeNB to the target DeNB is transparent to the UEs which aresubordinate to the mobile relay node. However, a fundamental objectiveof the RN handover is to provide the handover for UEs served by themobile relay node, and thus the target DeNB has to decide whether itaccepts or rejects each UE. But, currently there is not solution for thetarget DeNB to decide the UE handover.

Accordingly, it is required for the target DeNB to acknowledge the UEcontext.

SUMMARY OF INVENTION Technical Problem

The present invention provides a method and apparatus for determininghandover of user equipments access to mobile relay nodes in wirelesscommunication system. The present invention provides a method fortransmitting a UE context to a target DeNB for determining whether toaccept or reject each UE.

Solution to Problem

In an aspect, a method for determining, by a target donor eNodeB (DeNB),handover of user equipments (UEs) attached to a mobile relay node (RN),which is moving from a source DeNB to the target DeNB, in a wirelesscommunication system is provided. The method includes receiving ahandover request message from a RN mobility management entity (MME),receiving an indication including UE context of the UEs attach to themobile relay node from a UE mobility management entity (MME), anddetermining whether to accept or reject the handover of each UE.

In another aspect, a method for determining, by a target donor eNodeB(DeNB), handover of user equipments (UEs) attached to a mobile relaynode (RN), which is moving from a source DeNB to the target DeNB, in awireless communication system is provided. The method includes receivinga handover request message and an indication including UE context of theUEs attach to the mobile relay node from a RN mobility management entity(MME), and determining whether to accept or reject the handover of eachUE.

In another aspect, a method for determining, by a target donor eNodeB(DeNB), handover of user equipments (UEs) attached to a mobile relaynode (RN), which is moving from a source DeNB to the target DeNB, in awireless communication system is provided. The method includes receivinga handover request message from the source DeNB, transmitting a requestfor an indication including UE context of the UEs attach to the mobilerelay node to a UE mobility management entity (MME), receiving theindication including the UE context of the UEs attach to the mobilerelay node from the UE MME, and determining whether to accept or rejectthe handover of each UE.

Advantageous Effects of Invention

A target DeNB can accept or reject each UE attached to a mobile relaynode, which attempts to perform a handover to the target DeNB, based ona UE context.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows network structure of an evolved universal mobiletelecommunication system (E-UMTS).

FIG. 2 shows architecture of a typical E-UTRAN and a typical EPC.

FIG. 3 shows a user-plane protocol and a control-plane protocol stackfor the E-UMTS.

FIG. 4 shows an example of structure of a physical channel.

FIG. 5 shows an objective of relay.

FIG. 6 shows an overall E-UTRAN architecture supporting relay nodes.

FIG. 7 shows an example of deployments scenario of mobile relay node ata high speed train.

FIG. 8 shows an example of a mobile relay node architecture.

FIG. 9 shows another example of a mobile relay node architecture.

FIG. 10 shows an example of a method of transmitting an indicationincluding a UE context according to an embodiment of the presentinvention.

FIG. 11 shows another example of a method of transmitting an indicationincluding a UE context according to an embodiment of the presentinvention.

FIG. 12 shows another example of a method of transmitting an indicationincluding a UE context according to an embodiment of the presentinvention.

FIG. 13 is a block diagram showing wireless communication system toimplement an embodiment of the present invention.

MODE FOR THE INVENTION

The technology described below can be used in various wirelesscommunication systems such as code division multiple access (CDMA),frequency division multiple access (FDMA), time division multiple access(TDMA), orthogonal frequency division multiple access (OFDMA), singlecarrier frequency division multiple access (SC-FDMA), etc. The CDMA canbe implemented with a radio technology such as universal terrestrialradio access (UTRA) or CDMA-2000. The TDMA can be implemented with aradio technology such as global system for mobile communications(GSM)/general packet ratio service (GPRS)/enhanced data rate for GSMevolution (EDGE). The OFDMA can be implemented with a radio technologysuch as institute of electrical and electronics engineers (IEEE) 802.11(Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, evolved UTRA (E-UTRA), etc.IEEE 802.16m is an evolution of IEEE 802.16e, and provides backwardcompatibility with an IEEE 802.16-based system. The UTRA is a part of auniversal mobile telecommunication system (UMTS). 3rd generationpartnership project (3GPP) long term evolution (LTE) is a part of anevolved UMTS (E-UMTS) using the E-UTRA. The 3GPP LTE uses the OFDMA indownlink and uses the SC-FDMA in uplink. LTE-advance (LTE-A) is anevolution of the 3GPP LTE.

For clarity, the following description will focus on the LTE-A. However,technical features of the present invention are not limited thereto.

In general, when UE performs handover, a target eNB may accept or rejectthe UE's handover depending on its current state. At this time, thetarget eNB may determine the current state using UE context and mayaccept or reject the UE's handover. The UE context may include anE-UTRAN radio access bearer (E-RAB) identifier (ID) that should be usedby the UE and quality of service (QoS)-related parameters of thecorresponding E-RAB. The target eNB may determine whether to be able toassign resources to E-RABs having a specific QoS included in the UEcontext and may accept or reject the UE's handover.

Likewise, in case a mobile relay node performs handover, a target DeNBsupporting the mobile relay node may accept or reject the handover ofthe mobile relay node according to the current state. At this time, thetarget DeNB may determine the current state using RN context and mayaccept or reject the mobile relay node's handover. On the other hand,when the mobile relay node performs handover, handover for UEs attachedto the mobile relay node is carried out, so that the target DeNB needsto support group mobility for the UEs. The target DeNB should accept orreject the handover for each of the UEs attached to the mobile relaynode using the UE contexts of the corresponding UEs.

Table 1 shows whether the source DeNB and the target DeNB have RNcontexts and UE contexts depending on the type of the handover andmobile relay architectures shown in FIGS. 8 and 9. At this time, it isassumed that both S1-based handover and X2-based handover are supportedfor the UEs attached to the mobile relay node. In Table 1, Alt. 1represents the case of the mobile relay architecture shown in FIG. 8,and Alt. 2 represents the case of the mobile relay architecture shown inFIG. 9.

TABLE 1 Alt. 1 Alt. 2 Source Target Source Target DeNB DeNB DeNB DeNB X2handover RN context RN context RN context RN context (∘) (∘) (∘) (∘) UEcontext (x) UE context UE context UE context RN context (x) (∘) (x) (∘)S1 handover RN context RN context RN context (∘) (∘) (∘) UE context (x)UE context UE context UE context (x) (∘) (x)

Referring to Table 1, when the mobile relay node moves from the sourceDeNB to the target DeNB, the source DeNB and the target DeNB have RNcontexts at any case irrespective of the type of handover and the mobilerelay architecture. This is why to support mobility of the mobile relaynode, the source DeNB and the target DeNB need the RN contexts. However,in the mobile relay architecture shown in FIG. 8, the source DeNB andthe target DeNB cannot have UE contexts at any case regardless of thetype of handover. This is because in the mobile relay architecture shownin FIG. 8 SGW/PGW of the mobile relay node is not positioned inside theDeNB and thus the source DeNB and the target DeNB cannot be aware of UEcontexts. Further, also in the mobile relay architecture shown in FIG.9, the target DeNB cannot have UE contexts at any case irrespective ofthe type of handover. This is because the source DeNB may be aware of UEcontexts by SGW/PGW of a mobile relay node positioned therein, but thetarget DeNB has no way to receive it while performing handover.

As described above, when the mobile relay node is on the move from thesource DeNB to the target DeNB, the target DeNB does not have UEcontexts of the UEs attached to the mobile relay node at any case. Ifthe target DeNB is not aware of UE contexts, when the UEs attached tothe mobile relay node performs handover to the target DeNB, the targetDeNB cannot determine whether to accept or reject the handover for eachof the UEs. If the mobile relay node performs handover to the targetDeNB without any measurement, all the UEs attached to the mobile relaynode turn into an out-of-service situation as the ongoing service isstopped, thus causing serious service interruption.

Accordingly, a method is required to inform the target DeNB of UEcontexts when the mobile relay node performs handover to the targetDeNB. If the target DeNB is aware of UE contexts of the UEs attached tothe mobile relay node, the target DeNB may accept or reject the handoverfor each of the UEs. If the target DeNB fails to have enough resourcesto be able to assign to all the UEs, the target DeNB may accept thehandover of some UEs and may reject the handover of other UEs.

According to an embodiment of the present invention, in case the mobilerelay node performs S1-based handover or X2-based handover from thesource DeNB to the target DeNB, an UE MME recognizes the handover of themobile relay node and may transmit an indication including UE contextsto the target DeNB for handover of the UEs attached to the mobile relaynode. The UE contexts may include E-RAB IDs that should be used by theUEs and QoS-related parameters of corresponding E-RABs. Hereinafter,this is described through various embodiments.

FIG. 10 shows an example of a method of transmitting an indicationincluding a UE context according to an embodiment of the presentinvention. The embodiment of FIG. 10 shows the case of S1-basedhandover.

Referring to FIG. 10, in step S100, the source DeNB transmits a handoverrequired message to an RN MME. In step S110, the RN MME transmits ahandover request message to the target DeNB in response to the handoverrequired message.

In step S120, a UE MME recognizes that the mobile relay node performshandover to the target DeNB by various methods. Accordingly, in stepS130, the UE MME directly transmits an indication including the UEcontext to the target DeNB. The indication may be transmitted through anexisting message or a newly defined message. The UE MME has the UEcontext irrespective of the mobile relay architecture and thus mayprovide information of the UEs attached to the mobile relay node to thetarget DeNB. In the embodiment of FIG. 10, it is assumed that after thehandover request message is transmitted the indication including the UEcontext is transmitted. However, the indication including the UE contextmay be transmitted earlier than the handover request message.

In step S140, the target DeNB may accept or reject the handover of eachUE based on the UE context included in the indication received from theUE MME.

FIG. 11 shows another example of a method of transmitting an indicationincluding a UE context according to an embodiment of the presentinvention. The embodiment of FIG. 11 shows the case of S1-basedhandover.

Referring to FIG. 11, in step S200, the source DeNB transmits a handoverrequired message to the RN MME.

In step S210, the UE MME recognizes that the mobile relay node performshandover to the target DeNB by various methods. Accordingly, in stepS220, the UE MME transmits an indication including the UE context to theRN MME. The indication may be transmitted through an existing message ora newly defined message.

In step S230, the RN MME transmits the indication received from the UEMME, together with a handover request message which is a response to thehandover required message, to the target DeNB.

In step S240, the target DeNB may accept or reject the handover of eachUE based on the UE context included in the indication received from theRN MME.

FIG. 12 shows another example of a method of transmitting an indicationincluding a UE context according to an embodiment of the presentinvention. The embodiment of FIG. 12 shows the case of X2-basedhandover.

Referring to FIG. 12, in step S300, the source DeNB transmits a handoverrequest message to the target DeNB.

In step S310, the target DeNB directly sends a request for transmittingan indication including the UE context to the UE MME. The request may betransmitted through an existing message or a newly defined message. Instep S320, the UE MME receives the request from the target DeNB andtransmits the indication including the UE context to the target DeNB.The indication may be transmitted through an existing message or a newlydefined message.

In step S330, the target DeNB may accept or reject the handover of eachUE based on the UE context included in the indication received from theUE MME.

FIG. 13 is a block diagram showing wireless communication system toimplement an embodiment of the present invention.

A target DeNB 800 includes a processor 810, a memory 820, and an RF(radio frequency) unit 830. The processor 810 may be configured toimplement proposed functions, procedures, and/or methods in thisdescription. Layers of the radio interface protocol may be implementedin the processor 810. The memory 820 is operatively coupled with theprocessor 810 and stores a variety of information to operate theprocessor 810. The RF unit 830 is operatively coupled with the processor810, and transmits and/or receives a radio signal.

A UE MME 900 may include a processor 910, a memory 920 and a RF unit930. The processor 910 may be configured to implement proposedfunctions, procedures and/or methods described in this description.Layers of the radio interface protocol may be implemented in theprocessor 910. The memory 920 is operatively coupled with the processor910 and stores a variety of information to operate the processor 910.The RF unit 930 is operatively coupled with the processor 910, andtransmits and/or receives a radio signal.

The processors 810, 910 may include application-specific integratedcircuit (ASIC), other chipset, logic circuit and/or data processingdevice. The memories 820, 920 may include read-only memory (ROM), randomaccess memory (RAM), flash memory, memory card, storage medium and/orother storage device. The RF units 830, 930 may include basebandcircuitry to process radio frequency signals. When the embodiments areimplemented in software, the techniques described herein can beimplemented with modules (e.g., procedures, functions, and so on) thatperform the functions described herein. The modules can be stored inmemories 820, 920 and executed by processors 810, 910. The memories 820,920 can be implemented within the processors 810, 910 or external to theprocessors 810, 910 in which case those can be communicatively coupledto the processors 810, 910 via various means as is known in the art.

In view of the exemplary systems described herein, methodologies thatmay be implemented in accordance with the disclosed subject matter havebeen described with reference to several flow diagrams. While forpurposed of simplicity, the methodologies are shown and described as aseries of steps or blocks, it is to be understood and appreciated thatthe claimed subject matter is not limited by the order of the steps orblocks, as some steps may occur in different orders or concurrently withother steps from what is depicted and described herein. Moreover, oneskilled in the art would understand that the steps illustrated in theflow diagram are not exclusive and other steps may be included or one ormore of the steps in the example flow diagram may be deleted withoutaffecting the scope and spirit of the present disclosure.

1. A method for determining, by a target donor eNodeB (DeNB), handoverof user equipments (UEs) attached to a mobile relay node (RN), which ismoving from a source DeNB to the target DeNB, in a wirelesscommunication system, the method comprising: receiving a handoverrequest message from a RN mobility management entity (MME); receiving anindication including UE context of the UEs attach to the mobile relaynode from a UE mobility management entity (MME); and determining whetherto accept or reject the handover of each UE.
 2. The method of claim 1,wherein the UE context includes an evolved UMTS terrestrial radio accessnetwork (E-UTRAN) radio access bearer (E-RAB) identifier (ID) for eachUE, and quality of service (QoS)-related parameters for the E-RAB ID. 3.The method of claim 1, wherein the indication is received through an S1interface.
 4. The method of claim 1, wherein the indication is receivedafter receiving the handover request message.
 5. The method of claim 1,wherein the indication is received before receiving the handover requestmessage.
 6. A method for determining, by a target donor eNodeB (DeNB),handover of user equipments (UEs) attached to a mobile relay node (RN),which is moving from a source DeNB to the target DeNB, in a wirelesscommunication system, the method comprising: receiving a handoverrequest message and an indication including UE context of the UEs attachto the mobile relay node from a RN mobility management entity (MME); anddetermining whether to accept or reject the handover of each UE.
 7. Themethod of claim 6, wherein the UE context includes an evolved UMTSterrestrial radio access network (E-UTRAN) radio access bearer (E-RAB)identifier (ID) for each UE, and quality of service (QoS)-relatedparameters for the E-RAB ID.
 8. The method of claim 6, wherein thehandover request message and the indication are received through an S1interface.
 9. The method of claim 6, wherein the indication is received,by the RN MME, from a UE MME.
 10. A method for determining, by a targetdonor eNodeB (DeNB), handover of user equipments (UEs) attached to amobile relay node (RN), which is moving from a source DeNB to the targetDeNB, in a wireless communication system, the method comprising:receiving a handover request message from the source DeNB; transmittinga request for an indication including UE context of the UEs attach tothe mobile relay node to a UE mobility management entity (MME);receiving the indication including the UE context of the UEs attach tothe mobile relay node from the UE MME; and determining whether to acceptor reject the handover of each UE.
 11. The method of claim 10, whereinthe UE context includes an evolved UMTS terrestrial radio access network(E-UTRAN) radio access bearer (E-RAB) identifier (ID) for each UE, andquality of service (QoS)-related parameters for the E-RAB ID.
 12. Themethod of claim 10, wherein the handover request message is receivedthrough an X2 interface.